Studying venus using polarimetry

Abstract

Venus presents a compelling case study of the greenhouse effect, resulting in the highest surface temperatures of any planet in our solar system. Despite its similarities to Earth in origin and size, Venus has a vastly different atmosphere, dominated by CO2 and thick sulfuric acid clouds undergoing retrograde super-rotation. To better understand Venus’ climate and characterise it, this thesis employs the technique of polarimetry to develop precise computational models of light scattering in its atmosphere. These models are compared with existing observations to investigate dynamic atmospheric phenomena, such as gravity waves and variations in cloud top altitude. Planet-wide gravity waves were observed by the Japanese Akatsuki spacecraft in thermal infrared wavelengths on Venus. These waves were attributed to the underlying mountainous topography and are generated when wind flows over mountains and propagate to themiddle and upper cloud layers. In chapter 2, we explore the possibility of whether orographic gravity waves of similar nature would be observable through polarimetry. As gravity waves propagate, they alter atmospheric density and aerosol distribution, making them observable through various imaging techniques. While direct and thermal imaging have primarily been used to detect these waves, those affecting higher altitudes cause much smaller changes in atmospheric density as compared to the cloud tops. Consequently, these high-altitude waves are challenging to observe with direct imaging and have been detected primarily through in-situ sensors or night-glow measurements. Unlike direct imaging, which captures both polarized and unpolarized light, polarimetry is more sensitive to density variations due to the high degree of polarization imparted by gas molecules, which also varies with solar and viewing geometry.